In the event of a breakage in the enveloping bulb of halogen incandescent lamps with outer bulbs, there are two possible safety risks: (a) the lamp continues to burn, which can lead to a fire in the case of a luminaire that has fallen over, and (b) the electrical connections of the burner are still live, which can be particularly dangerous in the case of a defective burner. A conventional solution, in which a fuse, which is interconnected in series with the light source and is in the form of a filament in the lamp, burns through, disconnects the lamp too slowly to avoid risk (a). In addition, a marked loss of efficiency arose as a result of using the filament. At the present time, there is no satisfactory solution to electrical hazards that come under risk (b).
A tungsten-halogen lamp having a filament chamber which is permeable to light, provided with an IR coating and encloses an incandescent filament is disclosed in DE 43 37 807 A1, which lamp is enclosed within an outer bulb. Fuses are connected to the opposite ends of the incandescent filament in order to limit the size and duration of an electric arc across a breakage in the incandescent filament, which, in combination with a filling-gas pressure of not more than about 0.33 MPa (3300 mbar), is intended to reduce the probability of a failure of the container.